A NON-DOUBLE-COUPLE EARTHQUAKE IN A SUBDUCTING OCEANIC-CRUST OF THE PHILIPPINE SEA PLATE

被引：13

作者：

HURUKAWA, N

IMOTO, M

机构：

[1] International Institute of Seismology and Earthquake Engineering, Building Research Institute

[2] National Research Institute for Earth Science and Disaster Prevention

来源：

JOURNAL OF PHYSICS OF THE EARTH | 1993年 / 41卷 / 04期

关键词：

D O I：

10.4294/jpe1952.41.257

中图分类号：

P [天文学、地球科学];

学科分类号：

07 ;

摘要：

A non double-couple earthquake was found in an oceanic crust of the Philippine Sea plate subducting into the mantle in the Kanto district, central Japan. Its magnitude and focal depth are 4.6 and 57 km, respectively. This subducting oceanic crust consists of low-density gabbro or basalt at depths shallower than about 60 km, while it consists of high-density eclogite to which gabbro transformed at depths deeper than about 60 km. The non double-couple earthquake occurred at this density boundary in the oceanic crust. Since the first motion of seismic P waves is predominantly dilatational and shows volume contraction, we consider that this event was probably caused by a sudden phase transformation from gabbro to eclogite. Its predominant frequency implies that this phase transformation occurred instantaneously in the metastability field. Since this event emanated not only compressional waves but also shear waves, we conclude that the sudden volume contraction triggered a double-couple earthquake immediately. This interpretation is supported by the aftershock distribution and the P-wave first-motion distribution of an eyeball type, which has only one cone on the focal sphere.

引用

页码：257 / 269

页数：13

共 25 条

[1]

Ahrens T.J., Schubert G., Gabbro-eclogite reaction rate and its geophysical significance, Rev. Geophys. Space Phys., 13, pp. 383-400, (1975)

[2]

Burnley P.C., Green H.W., Prior D.J., Faulting associated with the olivine to spinel transformation in Mg2GeO4 and its implications for deep-focus earthquakes, J. Geophys. Res., 96, pp. 425-443, (1991)

[3]

Dennis J.G., Walker C.T., Earthquakes resulting from metastable phase transitions, Tectonophysics, 2, pp. 401-407, (1965)

[4]

Green H.W., Burnley P.C., A new self-organizing mechanism for deep-focus earthquakes, Nature, 341, pp. 733-737, (1989)

[5]

Green H.W., Young T.E., Walker D., Scholz C.H., Anticrack-associated faulting at very high pressure in natural olivine, Nature, 348, pp. 720-722, (1990)

[6]

Green H.W., Scholz C.H., Tingle T.N., Young T.E., Koczynski T.A., Acoustic emissions produced by anticrack faulting during the olivine spinel transformation, Geophys. Res. Lett., 19, pp. 789-792, (1992)

[7]

Hamada K., Ohtake M., Okada Y., Matsumura S., Sato H., A high quality digital network for microearthquakes and ground tilt observations in the Kanto-Tokai area, Earthq. Predict. Res., 3, pp. 447-469, (1985)

[8]

Hori S., Seismic waves guided by untransformed oceanic crust subducting into the mantle: the case of the Kanto district, Tectonophysics, 176, pp. 355-376, (1990)

[9]

Hurukawa N., Imoto M., Fine structure of an underground boundary between the Philippine Sea and Pacific plates beneath the Kanto district, Zisin (J. Seismol. Soc. Jpn.), 43, pp. 413-429, (1990)

[10]

Hurukawa N., Imoto M., Subducting oceanic crusts of the Philippine Sea and Pacific plates and weak-zone-normal compression in the Kanto district, Geophys. J. Int., 109, pp. 639-652, (1992)

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